Locally deformable sleeve on disk drive pivot assembly

ABSTRACT

A disk drive pivot assembly has a locally deformable internal sleeve that is equipped with two small deformable zones where the sleeve makes contact with the actuator comb bore. The zones can be in the shape of two rings with a rectangular or circular cross-sectional shape. The material may include zinc, magnesium, copper, or aluminum, or their alloys. These materials are relatively soft and have a relatively low stiffness compared to the comb bore. The thickness of the rings may range from approximately 0.25 to 1.0 mm, and they may be attached via shrink fit or adhesive bonding.

BACKGROUND OF THE INVENTION

[0001] 1. Technical Field

[0002] The present invention relates in general to an improved diskdrive pivot sleeve, and in particular to an improved disk drive pivotassembly with a locally deformable sleeve.

[0003] 2. Description of the Related Art

[0004] Generally, a data access and storage system consists of one ormore storage devices that store data on magnetic or optical storagemedia. For example, a magnetic storage device is known as a directaccess storage device (DASD) or a hard disk drive (HDD) and includes oneor more disks and a disk controller to manage local operationsconcerning the disks. The hard disks themselves are usually made ofaluminum alloy or a mixture of glass and ceramic, and are covered with amagnetic coating. Typically, two or three disks are stacked verticallyon a common spindle that is turned by a disk drive motor at severalthousand revolutions per minute (rpm).

[0005] The only other moving part within a typical HDD is the actuatorassembly. The actuator moves magnetic read/write heads to the desiredlocation on the rotating disk so as to write information to or read datafrom that location. Within most HDDs, the magnetic read/write head ismounted on a slider. A slider generally serves to mechanically supportthe head and any electrical connections between the head and the rest ofthe disk drive system. The slider is aerodynamically shaped to glideover moving air in order to maintain a uniform distance from the surfaceof the rotating disk, thereby preventing the head from undesirablycontacting the disk.

[0006] Typically, a slider is formed with an aerodynamic pattern ofprotrusions (air bearing design) on its air bearing surface (ABS) thatenables the slider to fly at a constant height close to the disk duringoperation of the disk drive. A slider is associated with each side ofeach platter and flies just over the platter's surface. Each slider ismounted on a suspension to form a head gimbal assembly (HGA). The HGA isthen attached to a semi-rigid actuator arm that supports the entire headflying unit. Several semi-rigid arms may be combined to form a singlemovable unit having either a linear bearing or a rotary pivotal bearingsystem.

[0007] The head and arm assembly is linearly or pivotally movedutilizing a magnet/coil structure that is often called a voice coilmotor (VCM). The stator of a VCM is mounted to a base plate or castingon which the spindle is also mounted. The base casting with its spindle,actuator VCM, and internal filtration system is then enclosed with acover and seal assembly to ensure that no contaminants can enter andadversely affect the reliability of the slider flying over the disk.When current is fed to the motor, the VCM develops force or torque thatis substantially proportional to the applied current. The armacceleration is therefore substantially proportional to the magnitude ofthe current. As the read/write head approaches a desired track, areverse polarity signal is applied to the actuator, causing the signalto act as a brake, and ideally causing the read/write head to stopdirectly over the desired track.

[0008] Actuator assemblies typically utilize a comb-like structure thatare formed from very stiff materials in order to increase servobandwidth. These classes of materials, such as ceramics, metal matrixcomposites, and beryllium alloys, are up to five times stiffer and fivetimes harder than aluminum. One common means to attach a pivot to a combis to use a small screw to either push or pull the pivot into ascalloped portion of the comb bore. Due to slight geometricalimperfections (tolerances) of the pivot and comb bore, the parts do notmake ideal and uniform contact. Fortunately, the elastic nature ofaluminum comb bodies and pivot sleeves allow them to locally deform asmall but sufficient amount at the points of contact, therebyeffectively distributing the loads evenly among lines of contact.

[0009] Problems arise when a stiffer comb body does not locally deformagainst the pivot bearing sleeve, thus causing non-uniform loads at thelines of contact. The problem is exacerbated when the pivot sleeve isalso made of the same high stiffness material in order to match thecoefficient of thermal expansion of the comb and it can no longerlocally deform against the comb bore. When this condition exists, theactuator is dynamically unstable because the comb and sleeve oscillateslightly with respect to each other under seek conditions. Seek energycauses the comb to rock on the pivot at the points with the highestloads. This instability will cause track misregistration at current andfuture track pitches. Thus, an improved disk drive pivot assembly isneeded.

SUMMARY OF THE INVENTION

[0010] One embodiment of an improved disk drive pivot assembly has alocally deformable internal sleeve. The sleeve is equipped with twosmall deformable zones where the sleeve makes contact with the actuatorcomb bore. The zones can be in the shape of two rings with a rectangularor circular cross-sectional shape. The material may include zinc,magnesium, copper, or aluminum, or their alloys. These materials arerelatively soft and have a relatively low stiffness compared to the combbore. The thickness of the rings may range from approximately 0.25 to1.0 mm, and they may be attached via shrink fit or adhesive bonding.

[0011] The foregoing and other objects and advantages of the presentinvention will be apparent to those skilled in the art, in view of thefollowing detailed description of the preferred embodiment of thepresent invention, taken in conjunction with the appended claims and theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] So that the manner in which the features, advantages and objectsof the invention, as well as others which will become apparent, areattained and can be understood in more detail, more particulardescription of the invention briefly summarized above may be had byreference to the embodiment thereof which is illustrated in the appendeddrawings, which drawings form a part of this specification. It is to benoted, however, that the drawings illustrate only a preferred embodimentof the invention and is therefore not to be considered limiting of itsscope as the invention may admit to other equally effective embodiments.

[0013]FIG. 1 is a plan view of a disk drive assembly with a coverremoved to show the principle subassembly.

[0014]FIG. 2 is a side view of one embodiment of a pivot assemblyconstructed in accordance with the present invention.

[0015]FIG. 3a is an enlarged side view of the pivot assembly of FIG. 2showing a deformable ring with a seated rectangular cross-section.

[0016]FIG. 3b is an enlarged side view of the pivot assembly of FIG. 2showing a deformable ring with a seated semi-circular cross-section.

[0017]FIG. 3c is an enlarged side view of the pivot assembly of FIG. 2showing a deformable ring with a surface-mounted rectangularcross-section.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE PRESENTINVENTION

[0018] Referring to FIG. 1, a schematic drawing of one embodiment of aninformation storage system comprising a magnetic hard disk file or drive111 for a computer system is shown. Drive 111 has an outer housing orbase 113 containing a plurality of stacked, parallel magnetic disks 115(one shown) which are closely spaced apart. Disks 115 are rotated by aspindle motor assembly 131 having a central drive hub 117. An actuator121 comprises a plurality of parallel actuator arms 125 (one shown) inthe form of a comb that is pivotally mounted to base 113 about a pivotassembly 123. A controller 119 is also mounted to base 113 forselectively moving the comb of arms 125 relative to disks 115.

[0019] In the embodiment shown, each arm 125 has extending from it atleast one cantilevered load beams or suspensions 127, a magneticread/write transducer or head 129 mounted on a slider secured to aflexure that is flexibly mounted to each suspension 127. The read/writeheads 129 magnetically read data from and/or magnetically write data todisks 115. The level of integration called head gimbal assembly is head129 and the slider are mounted on suspension 127. Suspensions 127 have aspring-like quality which biases or urges the slider against the disk toenable the creation of the air bearing film between the slider and disksurface. A voice coil 133 housed within a conventional voice coil motormagnet assembly 134 (top pole not shown) is also mounted to arms 125opposite the head gimbal assemblies. Movement of the actuator 121(indicated by arrow 135) by controller 119 moves head gimbal assemblies129 radially across tracks on the disks 115 until the heads 129 settleon the target tracks. The head gimbal assemblies operate in aconventional manner and always move in unison with one another, unlessdrive 111 uses multiple independent actuators (not shown) wherein thearms can move independently of one another.

[0020] Referring now to FIG. 2, a side view of pivot assembly 123 isshown. Pivot assembly 123 comprises a shaft 141 mounted within the boreof a sleeve 143. Sleeve 143 has a cylindrical exterior surface and ispreferably formed from a very stiff material such as ceramics, ceramiccomposites, metal matrix composites, or beryllium alloys. Sleeve 143 hasat least one deformable zone 145 (two shown). In the embodiment shown,zones 145 are axially spaced apart from each other, and each zone 145circumscribes the exterior of sleeve 143. In the preferred embodiment,each zone 145 comprises a continuous ring that is mounted to sleeve 143.

[0021] As shown in FIGS. 3a-3 c, the rings may have variouscross-sectional shapes, including rectangular and semi-circular shapes.In addition, the rings may be seated within grooves or “rat bite”contact areas (FIGS. 3a and 3 b) in the exterior of sleeve 143, orsurface-mounted (FIG. 3c) to the exterior of sleeve 143 via shrink fit,adhesive bonding, etc. The rings of zones 145 are preferably formed froma relatively softer and low stiffness (Young's modulus) material thanthat of sleeve 143, such as zinc, magnesium, aluminum, copper, or theiralloys. The thickness (in the radial direction) of each ring is in therange of 0.25 to 1.0 mm.

[0022] Transfer function analysis is a convenient way to measure theeffect of the pivot-comb boundary condition on the actuator dynamics.The design of the present invention was tested with different materialsand transfer functions were derived. In one application, the actuatorhad a pivot with a stainless steel sleeve, and in a second applicationthe actuator had a pivot with an aluminum sleeve. The transfer functionswere nearly identical with very clean butterfly resonance modes and onlyone peak at 72 dB. The second resonance (arm S-mode) was around 55 to 57dB. In a soft aluminum comb bore, the pivot seats well regardless of thepivot sleeve material stiffness.

[0023] In addition, two transfer functions for the same head spindleassembly having an actuator comb formed from an alloy of 62% berylliumand 38% aluminum. This alloy is 2.8 times stiffer than an aluminum comb.In the first transfer function, the actuator had the same stainlesssteel pivot used with the aluminum comb, while in the second transferfunction, the actuator had the same aluminum pivot used with thealuminum comb. There was a significant difference between the twotransfer functions. With the stainless steel pivot, the first resonance(butterfly mode) broke into three peaks and is lower in amplitude.Moreover, the second resonance (arm S-mode) is lower in amplitude. Thetransfer functions were similar to those of a “mushy pivot” (i.e., anexcessively compliant pivot due to low stiffness) actuator. When thestainless steel pivot was replaced with an aluminum pivot, the transferfunction cleaned up.

[0024] This result is counterintuitive to what one skilled in the artwould expect because a sleeve with a lower Young's modulus shouldcontribute to pivot “mushiness.” Surprisingly, the head spindle assemblytransfer function with the aluminum pivot had a first resonance that hadonly one 5 dB higher amplitude peak, and a second resonance that was 5dB higher in amplitude. This phenomenon was repeatable for three otherstiff comb materials, namely, AlBC, AlSiC, and Al-65%Be. The phenomenonwas repeatable for three stainless steel pivots and three aluminumpivots. These data confirm that a deformable metal, such as aluminum,seats better against a hard, stiff comb bore providing better and moreconsistent boundary conditions resulting in improved actuator dynamics.

[0025] The present invention has several advantages including thermaland dynamic compatibility with a relatively high stiffness actuatorcomb. The very stiff pivot sleeve has deformable zones or bands that areformed from a relatively softer and low stiffness material. Thethickness of the bands is thick enough only to accommodate complianceand a snug fit between the sleeve and comb. Thus, the deformable metalbands deform between the stiffer sleeve and the stiffer bore to seatbetter against the bore to provide more consistent boundary conditionsto improve the overall dynamics of the actuator.

[0026] While the invention has been shown or described in only some ofits forms, it should be apparent to those skilled in the art that it isnot so limited, but is susceptible to various changes without departingfrom the scope of the invention.

What is claimed is:
 1. A pivot assembly for a disk drive actuator comb,comprising: a sleeve having an internal bore; a shaft mounted within thebore of the sleeve; a deformable zone on the sleeve, the deformable zonebeing formed from a material that is relatively softer and has lowerstiffness than a material of the sleeve; and wherein the deformable zoneis adapted to deform between the sleeve and a bore of the comb toprovide more consistent boundary conditions that results in improvedactuator dynamics.
 2. The pivot assembly of claim 1 wherein thedeformable zone circumscribes an external surface of the sleeve.
 3. Thepivot assembly of claim 1 wherein the deformable zone is a continuousring.
 4. The pivot assembly of claim 1 wherein the deformable zone has arectangular cross-sectional shape.
 5. The pivot assembly of claim 1wherein the deformable zone has a semicircular cross-sectional shape. 6.The pivot assembly of claim 1 wherein the deformable zone is seatedwithin a groove in the sleeve.
 7. The pivot assembly of claim 1 whereinthe deformable zone is surface-mounted to the sleeve.
 8. The pivotassembly of claim 1 wherein the deformable zone is formed from amaterial selected from the group consisting of zinc, magnesium,aluminum, copper, and their alloys.
 9. The pivot assembly of claim 1wherein the deformable zone has a thickness in the range of 0.25 to 1.0mm.
 10. The pivot assembly of claim 1 wherein the sleeve is formed froma material selected from the group consisting of ceramics, ceramiccomposites, metal matrix composites, and beryllium alloys.
 11. A pivotassembly for a disk drive actuator comb, comprising: a sleeve having acylindrical external surface and an internal bore; a shaft mountedwithin the bore of the sleeve; at least two deformable, continuous ringsmounted to and circumscribing the external surface of the sleeve, thedeformable rings being axially spaced apart from each other and formedfrom a material that is relatively softer and has lower stiffness than amaterial of the sleeve; and wherein the deformable rings are adapted todeform between the sleeve and a bore of the comb to provide moreconsistent boundary conditions that results in improved actuatordynamics.
 12. The pivot assembly of claim 11 wherein each of the ringshas a rectangular cross-sectional shape.
 13. The pivot assembly of claim11 wherein each of the rings has a semi-circular cross-sectional shape.14. The pivot assembly of claim 11 wherein each of the rings is seatedwithin a groove in the sleeve.
 15. The pivot assembly of claim 11wherein each of the rings is surface-mounted to the sleeve.
 16. Thepivot assembly of claim 11 wherein each of the rings is formed from amaterial selected from the group consisting of zinc, magnesium,aluminum, copper, and their alloys.
 17. The pivot assembly of claim 11wherein each of the rings has a thickness in the range of 0.25 to 1.0mm.
 18. The pivot assembly of claim 11 wherein the sleeve is formed froma material selected from the group consisting of ceramics, ceramiccomposites, metal matrix composites, and beryllium alloys.
 19. A diskdrive actuator, comprising: an actuator comb having an internal bore; asleeve mounted inside the comb bore and having a cylindrical externalsurface and an internal bore; a shaft mounted within the sleeve bore; atleast two deformable, continuous rings mounted to and circumscribing theexternal surface of the sleeve, the deformable rings being axiallyspaced apart from each other and formed from a material that isrelatively softer and has lower stiffness than a material of the sleeve;and wherein the deformable rings deform between the sleeve and the combbore when the sleeve is mounted within the comb bore to provide moreconsistent boundary conditions that results in improved actuatordynamics.
 20. The disk drive actuator of claim 19 wherein each of therings is formed from a material selected from the group consisting ofzinc, magnesium, aluminum, copper, and their alloys.
 21. The disk driveactuator of claim 19 wherein the sleeve is formed from a materialselected from the group consisting of ceramics, ceramic composites,metal matrix composites, and beryllium alloys.